POLYMNIA (or Polyhymnia) was one of the nine Mousai (Muses), the goddesses of music, song and dance. In Classical times, when the Mousai were assigned specific artistic and literary spheres, Polyhymnia was named Muse of religious hymns. In this guise she portrayed as a woman standing in a pensive or meditative. Her name was derived from the Greek words poly-, "many," and hymnos, "praise" or "hymn."

ENCYCLOPEDIA

POLY′MNIA or POLYHY′MNIA (Polumnia), a daughter of Zeus, and one of the nine Muses. She presided over lyric poetry, and was believed to have invented the lyre. (Hes. Theog. 78; Schol. ad Apollon. Rhod. iii. 1.) By Oeagrus she became the mother of Orpheus. (Schol. l. c. i. 23.) In works of art she was usually represented in a pensive attitude.

Diodorus Siculus, Library of History 4. 7. 1 (trans. Oldfather) (Greek historian C1st B.C.) :
"Hesiod even gives their [the Muses'] names when he writes: ‘Kleio, Euterpe, and Thaleia, Melpomene, Terpsikhore and Erato, and Polymnia, Ourania, Kalliope too, of them all the most comely.’
To each of the Mousai (Muses) men assign her special aptitude for one of the branches of the liberal arts, such as poetry, song, pantomimic dancing, the round dance with music, the study of the stars, and the other liberal arts . . . For the name of each Mousa (Muse), they say, men have found a reason appropriate to her: . . . Polymnia (Polyhymnia), because by her great (polle) praises (humnesis) she brings distinction to writers whose works have won for them immortal fame."

Ovid, Fasti 5. 9 ff (trans. Frazer) (Roman poetry C1st B.C. to C1st A.D.) :
"Declare to me, ye [the Mousai, Muses] who haunt the springs of Aganippian Hippocrene, those dear traces of the Medusaean steed [the origin of the name of the month of May]. The goddesses disagreed; of them Polyhymnia began the first; the others were silent, and noted her saying in their mind. ‘After chaos, as soon as the three elements were given to the world, and the whole creation resolved itself into new species . . .’ [She sings the song of creation and explains that the month of May was named for the goddess Majesta (Majesty).]"

Nonnus, Dionysiaca 5. 88 ff (trans. Rouse) (Greek epic C5th A.D.) :
"[At the wedding of Kadmos (Cadmus) and Harmonia:] The nine Mousai (Muses) too struck up a lifestirring melody: Polymnia nursingmother of the dance waved her arms, and sketched in the air an image of a soundless voice, speaking with hands and moving eyes in a graphic picture of silence full of meaning."